Better Looking (I): Hair, Eyes, Teeth, Nails

Transcription

1 1 Better Looking (I): Hair, Eyes, Teeth, Nails A small arrow printed before a word in the main text indicates that there is more information on that topic in the Glossary. News from the Future Global Times News, 21 March 2025 Dentist Numbers Fall Again For the fifth year running the number of registered dentists in Europe has declined and in some areas people are travelling up to 50 kilometres to obtain their services. The drop in numbers is blamed on the success of the new toothpastes such as LoveSmile that were launched 15 years ago. These not only keep teeth brilliantly white but contain nanoparticles which can penetrate cavities and repair them from the inside, so there is no longer a need for dentists to drill and fill. Dental work now mainly consists of fitting braces and occasionally mending broken teeth, said a leading professor at Rome s Dental School, adding: In my early days as a teacher I spent most of my time instructing students on how to repair or replace decayed teeth. Today a call for these services is almost unheard of. Even cosmetic treatment such as tooth whitening is rarely required. Modern toothpastes, first marketed in 2010, have been responsible for young people in Europe today having such wonderful teeth. They contained not only the usual cleaning agents and fluoride but included repairing additives such as nanoparticles of hydroxyapatite, the natural chemical from which tooth enamel is made. It is these which penetrate any tiny cavities and repair them. Products like LoveSmile also contain a whitening agent which prevents staining and, unlike the earlier whitening agents, it does not cause thinning of the outer layer of tooth enamel. Page 3: Chemicals in toothpaste could cause bone cancer in old age warns dental fillings manufacturer. Of course there is no such product as LoveSmile toothpaste, at least a search of the Internet failed to reveal one. What the above news item suggests is that a trip to the dentist is likely to become a rare event in the life of children born today, unlike the regular visits to the dentist that most people have had to make in the past if they wanted to keep their teeth in good condition. The new ingredients mentioned in the Better Looking, Better Living, Better Loving. John Emsley Copyright 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN

2 news item are already known and we will look at them later in this chapter, the theme of which is improving our looks with the help of various products that chemists have devised, namely hair colorants, hair restorers, contact lenses, tooth whiteners, and artificial fingernails. We begin with hair, regarded by many as their best asset, but it is possible to make it even more attractive. Crowning Glory Hair comes in various natural shades and colours, ranging from jet black through brown and auburn to ash blonde, which are produced by varying amounts of two pigments. These are slightly different versions of a biological polymer called melanin, one is black, and called eumelanin, and the other is blonde, and called phaeomelanin. Eumelanin particles predominate in black and brown hair, while phaeomelanin particles dominate in fair hair. These melanin pigments are incorporated into the hair as it grows, and the particles are formed in special cells called melanocytes. (When these cease to function then the hair they produce has no colour.) What our genes provide may not be quite what we want, and so we may seek to change the colour of our hair and this option is proving popular with young and old alike. Many will look to a hair stylist for advice, and they in their turn look to chemists to provide the necessary materials to make it possible. We can also purchase packs of these same chemicals and make the change ourselves. It will come as no surprise to learn that the global market for hair dyes exceeds $7 billion annually, and it continues to grow, with the US accounting for around a quarter. The first truly permanent hair dye was created by a French chemist, Eugène Schueller in 1907 who founded the French Harmless Hair Dye Company. Today we know it as L Oréal and it is still the biggest manufacturer of hair dyes with just over a third of world sales. Next comes Procter & Gamble with 13%, followed by Henkel with 11%, Wella with 9%, and Hoyu with 6%. Smaller producers account for the remaining 25%. Hair dyes are of three kinds: temporary, semi-permanent, and permanent. The first kind are easily washed out of the hair, the second will survive several washings but eventually fade, and the third are locked fast within the hair shaft and disappear only as the hair grows 10 Better Looking (I): Hair, Eyes, Teeth, Nails

3 out. What differentiates the various dyes is their chemistry, and it is the permanent type which is the most sophisticated chemically, although some people find this worrying more of that in a minute. First the good news. The dyes that are used for temporary colouring can be applied in the form of rinses, gels, mousses, and sprays. They coat the surface of the hair with dye and most of this will be washed away the next time the hair is shampooed. We may want this to occur if we have applied the dye for a special event such as a party, a fun day, or an on-stage performance. A typical temporary hair dye is the colorant known as FD&C Blue No.1. 1) This is a large molecule so it cannot penetrate into the hair, and it has three negatively charged groups of atoms which make it highly water soluble so it is easily washed off. Semi-permanent dyes are smaller molecules and these can pass through the outer layer of the hair, known as the cuticle, and move into the inner cortex, there to remain until they gradually leach out again and are washed away. A combination of dyes is generally required to produce the desired shade and those commonly used are listed in the Glossary. Chemicals destined to produce permanent hair dyes also penetrate the cuticle but then they become trapped by reacting together to form a much larger molecule which cannot escape. For this to happen the cuticle must be made permeable, which can be achieved by the action of a little ammonia (NH 3 ). This causes the hair shaft to swell by raising the ph to about 10, and this opens up the cuticle scales. Once inside the hair, the molecules react to form the dye molecule which is too large to escape when the scales close again under the action of a final rinse. Permanent hair colorants come as two separate gels which have to be mixed together before application. One contains hydrogen peroxide which serves two functions, one is to bleach away the natural melanins, the other is to activate PPD (short for paraphenylenediamine 2) ) which is then combined with a second molecule, known as a coupler, to form the dye. In fact there may be more than one type of coupler in a hair dye. For example, in L Oreal s dye Havana there are three couplers 3) which together generate a pale auburn shade referred to as light amber. 1) FD&C refers to the US Federal Food, Drugs, and Cosmetics Act. 2) Also called 1,4-benzenediamine. 3) These are 4-amino-phenol, 4-amino-2- hydroxy-toluene, and 3-amino-phenol. Crowning Glory 11

4 That was the good news now the bad news: There is another type of hair colorant which is generally aimed at men who are going grey and is based on lead acetate. Although it is poisonous it is regarded as safe because the metal is not absorbed through the skin. The dye is rubbed on the hair with which it reacts to form a black pigment. With each application the hair gets darker and darker until all the grey hairs have disappeared. Such treatments date back to the days of the Roman Empire, when combs made of lead were used and were dipped in vinegar. The acetic acid of the vinegar dissolved a little of the lead, which was then transferred to the hair. For the past 200 years or so the preferred treatment has been to dab a solution of lead acetate directly onto the hair, and such products are still available. Soon they are to be banned inside the EU on the grounds that lead is inherently dangerous. More serious perhaps are the charges that permanent hair dyes may cause cancer, they have even killed those who used them. Although PPD has been an ingredient of hair dyes for more than 30 years it has not been without occasional bad publicity due to an allergic reaction in some people. We now know that this type of allergy affects only three women in a million, and it has been traced to a rare genetic susceptibility. Many years ago it was claimed that as many as one woman in a hundred was sensitive to PPD. This turned out to be somewhat of an exaggeration and came from tests in which pure PPD was applied directly to the skin and then covered with a plastic patch. Nevertheless, users of these dyes are warned that a skin allergy test must be carried out. Typically they are told to apply a penny-sized area of the dye to the skin behind the ear. When this has dried, a second coating of dye should be applied, and then left for 48 hours. If the skin becomes inflamed in any way then the dye must not be used. In May 2001 a Mrs Narinder Devi who lived in Birmingham, England, decided to dye her hair but she skipped the skin test. Sadly she suffered a massive anaphylactic shock from which she died. This was a rare example of a fatality following the use of a hair dye, although what ingredient caused it was never deduced. Other severe cases of allergic reaction continue to occur, although rarely with such a fatal outcome, and while these are widely publicised in the media, they are extremely rare. (Victims invariably settle out of court.) Of women who genuinely do test their skin for sensitivity, around 2% will observe a 12 Better Looking (I): Hair, Eyes, Teeth, Nails

5 slight positive effect and they are informed in the leaflet which comes with the hair dye that they must not use the product. The 1970s also saw claims that the various chemicals used in hair colorants caused cancers in laboratory animal tests when fed to them in large doses over a long period. Others reported that they caused mutations in bacteria. As a result the suspect ingredients were withdrawn. Although PPD was never implicated in these tests, the EU even introduced limits on PPD to the effect that no more than 6% can be present in hair colorant products. Tests showed that in a typical hair dyeing session a women would absorb some PPD (at most 36 mg) but in any case this was rapidly excreted in her urine. PPD has been thoroughly tested over many years, but that does not prevent scare stories about its use being circulated. PPD is manufactured on a large scale by the US chemical giant Du Pont and is mainly used to manufacture resins and polymers. That which is destined for inclusion in hair dyes is specially made by a different process that ensures it is absolutely pure and that it is free from any by-products that could cause adverse effects. What this means is that if there is a risk to health from exposure to PPD then it will be due to the PPD itself and not to some hidden cause. There is an alternative to PPD and that is TDS (short for toluene-2,5-diamine sulfate). This is less skin sensitive but produces shades of brown that are slightly redder. Hair dyes have come under attack many times from those who thought their use might have long term effects such as causing cancer. In 2001 an epidemiological report linked them to bladder cancer, while another in 2004 linked them to leukaemia. Both reports naturally attracted media interest, and continue to be quoted, despite the fact that similar, and often better conducted, studies found no such links. The leukaemia scare began with a paper in the American Journal of Epidemiology which reported a study of 769 adults with acute leukaemia and compared them with 623 adults who did not have leukaemia. The finding was that those who had used older-style permanent hair dyes in the 1980s were more at risk of leukaemia, although that risk was tiny. (There was no extra risk for those who used non-permanent dyes.) The paper attracted worldwide attention although it was a retrospective analysis, and the hair dyes it referred to were phased out more than 20 years ago. Crowning Glory 13

6 A survey in 2000, carried out in Los Angeles by a group at the University of Southern California School of Medicine, found a link with bladder cancer. It involved 1541 people with this condition and they were compared to 897 people who were not so afflicted. Adjustments were made to take into account smokers, who are liable to be more at risk of this disease in any case, and it found that those who used permanent hair dyes every month had a slightly higher risk of bladder cancer, especially if they had used hair dyes continuously for 15 or more years. Hairdressers had an even higher risk. This revelation prompted the Scientific Committee on Cosmetic Products and Non- Food Products of the EU (SCCNFP) to issue a discussion paper in February This was followed in December that year by a requirement that manufacturers must submit by July 2005 all their data on hair dyes together with studies to assess their safety in terms of cancer and toxicity. The outcome of this has yet to be published, but it will take the form of an approved list of hair dyes which will be issued in In 2004 another epidemiological study was undertaken of 459 cases of bladder cancer in New Hampshire, USA, by the Dartmouth Medical School at Lebanon, and they were matched against 665 people who did not have the disease. This study found that men who used hair dye were less likely to suffer bladder cancer, whereas for women there was a slightly higher risk, although in both cases the observations were not statistically significant. Another survey, this time of more than half a million women, and carried out by the American Cancer Society, found no link at all between hair dyes and bladder cancer. A survey of 608 Connecticut women with breast cancer and 609 women who were free of the disease, was carried out under the auspices of Yale School of Public Health with collaboration from the European Institute of Oncology in Italy, McGill University in Canada, and the US National Cancer Institute. This weighty team of international medics found no evidence that those who used hair dyes of either the temporary or permanent kind were in any way increasing their risk of having breast cancer, and they published their results in the European Journal of Cancer in August In 2003 another study was undertaken by the world-famous Karolinska Institute of Sweden and specifically looked at the incidence of all types of cancer in Swedish hairdressers, the group that was expected to be most at risk. 14 Better Looking (I): Hair, Eyes, Teeth, Nails

7 The medical records of 38,800 women and 6,800 men were consulted stretching back for 40 years and these found that there was a higher risk of cancer in the 1960s but not in subsequent years, and there was no increased incidence of bladder cancer among the hairdressers compared to the rest of the population. So what should we make of all this? The upshot of all this analysis would appear to be that modern hair dyes present no risk of causing cancer either among those who apply them or those on whose hair they are applied. If you are still not convinced that synthetic chemical dyes are safe, and yet you want to change the colour of your hair or hide any grey then you must perforce turn to the dyes of old see box but even some of these should come with test patches and a warning. Natural Hair Dyes A traditional hair dye is henna which is extracted from a privet-like shrub, Lawsonia inermis, which grows in India, Pakistan, and Egypt, and which produces the chemical lawsone. This acts as the dye molecule and its name is 2-hydroxy-1,4-naphthoquinone and it is also known as natural orange 6. Were it to be produced by a chemical company it would be banned because it would not pass today s stringent health and safety checks; it can cause allergies and asthma in some people. Moreover, as a colorant it gives unpredictable results. Not that this stops those who campaign on behalf of socalled green alternatives from advocating henna as a safe natural dye. Those who recommend henna claim it has other benefits such as preventing dandruff, killing head lice, and curing ringworm, but these claims are unproven and almost certainly unreliable. Other natural hair dyes that have been used down the centuries have been indigo (chemical name 2-[1,3- dihydro-3-oxo-2h-indol-2-ylidene]-1,2- dihydro-3h-indol-3-one) extracted from Indigofera, a plant of the pea family, and pyrogallol (chemical name 1,2,3-trihydroxybenzene) extracted from walnut shells. This last dye was banned for use in the EU in Lemon juice, saffron, cloves, and tea are other plant extracts used to change the colour or tint hair, but they are somewhat unreliable, and may even have no effect at all. Thinning on Top Few things are more eye-catching than well styled hair, and that is true for both men and women. But while a woman s hair remains a valuable asset to the end of her life, for many men it starts to disap- Thinning on Top 15

8 pear when they reach 30, and soon their baldness begins to send out a signal which they may not care to broadcast, especially if they still want to be seen as sexually attractive. Not that this should have bothered the Old Testament prophet Elisha but, like many men, he was surprisingly sensitive about his looks. When he was on a journey to Bethel, sometime around 850 BC, he was mocked by a group of young boys on account of his baldness, he was so upset by their remarks that he cursed them. Suddenly two she-bears emerged from a nearby wood and tore into the group, badly savaging 42 of the children or so it says in the Bible. 4) Neither cursing, nor praying, is the answer to baldness, whereas chemistry can offer a realistic chance of undoing the ravages of time. The average head has 100,000 follicles from which hair grows at the rate of 0.37 mm per day, amounting to around 14 cm per year (just under 6 inches). Every day we lose about 50 hairs and this is perfectly natural and occurs because a hair follicle enters a resting phase for a few weeks after it has been active for around three years. The old hair then falls out and a new growth phase begins, but the new hair may be somewhat different from the old hair. It may lack melanin so it appears white, or it may be thinner, in which case it is likely to be even thinner after the next resting phase, and eventually it may not even appear at all. Hair cells divide in the bulb at the bottom of the hair follicle and as they migrate upwards they deposit a layer of keratin to form a tube-like structure. The cells divide about once a day, which is rapid for the human body, and this is why chemotherapy treatment for cancer also affects them. Cancer cells divide as quickly as hair cells, so that drugs designed to prevent cancer cells dividing also stop hair cells from working. When these cannot divide, the follicle behaves as if it is in the resting phase and the existing shaft of hair comes loose. Male baldness manifests itself on the crown of the head and at the temples, and it will progress until most of the scalp is hairless. This loss of hair has little to do with lifestyle, but partly to do with race; baldness afflicts 50% of white males, 22% of orientals, and 18% of black males. Equally important are the man s genes which govern production of the male hormone testosterone and its conversion to its more active form di-hydro-testosterone 5) by the enzyme 5-α-reductase which 4) The Second Book of the Kings 2:23. 5) As its name implies this is testosterone with two extra hydrogen atoms attached. 16 Better Looking (I): Hair, Eyes, Teeth, Nails

9 regulates the functioning of several parts of the male body including the genitals and the growth of hair. This enzyme eventually causes the number of active hair follicles to decline, while those that are active spend less time in the growing phase and produce hair that is thinner. One of the paradoxes of dihydrotestosterone is that it reduces the growth of hair on the scalp but promotes growth of hair on the chin, chest, and groin. Men with naturally low levels of 5-α-reductase do not become bald as they age, and they have much less body hair than normal. Baldness is the legacy inherited from a man s parents and there used to be nothing that he could do about it, that is until the 1980s when something strange began to be reported: the hair of some bald men suddenly started to grow again. Throughout history there have been those who have sought to exploit men who were losing their hair by selling them expensive cures, none of which worked. Hippocrates in 400 BC recommended applying a poultice of pigeon droppings, horseradish, and nettles. Today many men benefit from two accidental discoveries, or rather from the side effects of two pharmaceutical products that they were prescribed by doctors for very different ailments. Men who were given them reported that the hair on their bald heads was reappearing. These products are now widely available and they are marketed under the names of Regaine (Rogaine in the US) and Propecia. Propecia is the hair restorer that depends for its effectiveness on the chemical finasteride, which was designed to treat swelling of the prostate, the gland that produces the fluid part of semen. Prostate enlargement results from an excess of dihydrotestosterone, and is a condition that manifests itself in many men over 65. Finasteride was devised by chemists of the drug company Merck Sharp & Dohme and the process for making it was published in 1986 in a paper in the Journal of Medicinal Chemistry. This also reported on the way the molecule attached itself to 5-α-reductase and by blocking this enzyme the level of dihydrotestosterone is reduced. The link between this hormone and an enlarged prostate had been noted more than a century ago, in that castrated males never suffered from an enlarged prostate. As the prostate grows larger it squeezes the urethra, the tube down which urine exits from the bladder and this causes difficulty in urinating and the need to pass water frequently. The prostate may also develop cancer and while this is not a particularly life-threatening cancer it only makes matters worse. Thinning on Top 17

10 The finasteride molecule has the same shape as testosterone it has a nitrogen atom in place of a carbon atom and it can fit into the enzyme s active site. The upshot is that the enzyme encircles the molecule thinking it has hold of testosterone but finds it cannot carry out the modification which it is supposed to perform. The enzyme clings on to the finasteride in the belief that it has the right molecule and the result is stalemate. Finasteride works mainly on the 5-α-reductase in the genital region, but it also moderates this hormone in the scalp as well, so that hair begins to grow again. This unexpected side effect eventually led to finasteride being available under two brand names: Proscar, which is prescribed for the treatment of enlarged prostate, and Propecia, which is prescribed to treat baldness. Within a few years Proscar was generating revenues of $500 million a year in the USA alone, and Propecia was eventually to equal this. Proscar tablets are blue and apple-shaped, and the dose is 5 mg. Propecia tablets are tan coloured and octagonal in shape, and the dose is 1 mg. Those taking finasteride are warned that it must be taken for three months for it to have any effect. Is Propecia an effective hair-restorer? The answer would appear to be yes, based on comparisons with a placebo, of which only 7% of men taking it said they noticed signs of regrowth, whereas 66% of men who were taking the real thing said there were visible signs of new hair. Interfering with a male hormone might have been expected to have another side effect, namely lowered sex drive. However, only 2% of men taking Propecia reported that this was so. Nevertheless, sexually active men who take Propecia should not risk impregnating their partner because if the fertilized egg is to be male then it may develop into a baby boy with some female characteristics. Finasteride must, of course, only be used by men, which is not the case for the other drug that acts to restore hair, and that is Regaine (Rogaine). This can be used by both men and women. Regaine is the brand name for minoxidil, a drug produced by the UpJohn Corporation of America, and one that was designed to reduce high blood pressure, which it does very well. As with finasteride, what its users hadn t expected to experience was a regrowth of the hair on their heads. Minoxidil was patented in 1967 although clinical trials for treating baldness with it were not undertaken until the 1980s. The drug is a vasodilator, in other words it relaxes constricted blood vessels thereby allowing blood to flow more easily round the body. Doses 18 Better Looking (I): Hair, Eyes, Teeth, Nails

11 of between 5 and 50 mg per day can be prescribed, patients generally starting on the lowest dose which is gradually increased. Minoxidil as a prescription drug is known as Loniten and is taken as a tablet twice a day. It is used when other drugs have failed to control a patient s high blood pressure or when this is rising rapidly. Minoxidil starts to work almost immediately and within an hour the blood pressure will fall markedly. One side effect is fluid retention, most noticeable as a swelling of the ankles, so that a diuretic is prescribed at the same time to enable the body to increase its output of urine. The other side effect, if minoxidil is taken for several weeks, is hair growth around the face, which may explain why some women are reluctant to take the drug even for high blood pressure. When minoxidil gets into the blood stream it passes a message to the lining of the blood vessels telling them to relax. It does this in several steps, ultimately leading to an opening of the channels that allow potassium ions to move through cell membranes and triggering the desired response. This is no doubt part of the way it works in hair follicles and, by increasing the blood supply there, it revitalises the formation of keratin. Why hair begins to re-grow on the heads of those taking minoxidil is still not truly understood, but it happens, and UpJohn sells the drug as a lotion containing 2% (for women) or 5% (for men). 6) It is applied directly to the scalp and needs to be used every day. It was the first drug the FDA approved for the treatment of hair loss and that was in the 1980s. Today there are several generic forms on sale, such as Alopexil, Lonolox, Prexidil, etc., and they are available as over-the-counter treatments, but Regaine is the market leader. Regaine is reputed not only to stop hair loss, which it does for 80% of men using it, but appears even to stimulate re-growth in some cases. Applied twice daily it should begin to produce visible results within three months, although it could take twice as long, and may never work for some. The most noticeable side effect is itchiness, but this will subside after a week or so. In 1985 Regaine was tested at the Glasgow Royal Infirmary hospital in Scotland on 66 volunteers aged between 18 and 50. Half were given Regaine and half were given a placebo to rub on their balding scalps. At first the effects were disap- 6) Minoxidil is a white crystalline solid which melts at 248 C, and while it is insoluble in water, it is perfectly soluble in propene glycol, and this is what the lotion contains. Thinning on Top 19

12 pointing for those using Regaine until it was applied twice daily, and this is now the recommended treatment. Somewhat perversely, it appears to those who start using Regaine that more of their hair is being lost. This is actually a sign that it is working and what they are seeing is hair follicles that have become dormant being activated again and the old hair displaced. Nor should they worry that the new hair is soft and downy; it becomes thicker and stronger as the treatment is continued. However, stop using Regaine and its effects will cease and its benefits will have disappeared within a few weeks. Neither it, nor Propecia, is a permanent cure for baldness but at least they offer men who become prematurely bald some hope of keeping a more youthful appearance. I Can See Clearly Now Boys don t make passes at girls who wear glasses went the old adage, so what did a young girl do who needed to wear spectacles? She left them at home when she went out looking for a boyfriend. Of course there was always a risk that if she found a boy she really liked, he might reject her when he eventually saw that she needed to wear glasses. Those were the days when young men could pick and choose because they were in short supply, millions having died in two world wars. Today, many men are surplus to requirements and women can be choosey, so men are the ones who don t want to be seen wearing glasses. In fact there is no need for either sex to wear them; they can wear contact lenses instead. Contact lenses come in a wide variety: there are soft lenses and hard lenses; there are some you can wear night and day for a month or more, and disposable ones that you need wear only for a day; there are lenses that let your eyes breathe; there are bifocal lenses; and there are even lenses to correct astigmatism, a condition of the lens of the eye which makes everything seem blurred. All are products of years of research by chemical companies like Novartis, Ciba Vision, and Wesley Jessen. There are even coloured lenses that can make blue eyes bluer, and sport lenses that enable tennis players to keep their eye on the ball by enhancing the colour of a yellow tennis ball relative to its surroundings. 20 Better Looking (I): Hair, Eyes, Teeth, Nails

13 The idea of contact lenses is not new. Leonardo da Vinci suggested them as long ago as 1508, although he never got around to making any. That did not happen until 1888, when a Dr F.A. Muller of Wiesbaden, Germany, made one from glass and it was worn by a patient of his who had no eyelids. The lens preserved the sight in one eye and he is said to have used it for 20 years. That same year a Dr Adolph Frick at the Ophthalmic Clinic in Zurich fitted six patients with glass contact lenses 1.4 cm in diameter (1/2 inch) and designed to cover the whole eye. They were not successful because he could not make them a perfect fit, though he made plaster casts of the eyes of cadavers, and even of his own eyes, to use as a template. His contact lenses were just too painful to wear. Despite the efforts of other doctors to make better impressions of eyeballs, there was no major advance in contact lens technology for another 50 years until they could be made of the polymer PMMA, short for poly(methyl methacrylate), which had been discovered at the laboratories of Rohm & Haas in Germany in the 1920s. They called the new polymer Plexiglas but it remained a curiosity because the chemical from which it was made was too expensive. That changed when chemist John Crawford, working for ICI in England, found a way to make methyl methacrylate cheaply from acetone, and the company named its PMMA Perspex. (In the USA it was called Lucite.) PMMA soon became a most profitable polymer, and it was ideal for all sorts of things such as illuminated signs, hospital incubators, car headlights, and aircraft windows. 7) It was ideal for contact lenses. What features should a contact lens have? Clearly it should be as transparent as glass, fit perfectly to the shape of the cornea, and be comfortable to wear. It should not harbour microbes that might cause eye infections, and it should be wearable for days without needing to be changed. It must not block off oxygen because the cornea of the eyeball needs a supply of this vital element. If it is to be disposable, it must be inexpensive. Producing a plastic with all these benefits has almost been achieved, thanks to polymer chemists. PMMA was the first major step forward. It has a refractive index like that of glass, in other words it makes a good lens because it can collect and focus light rays. 7) The Spitfire fighter planes of World War II had Perspex windows. When pilots were injured by splinters from them, surgeons noted that fragments could remain embedded within the body because this plastic is tolerated by living tissue. I Can See Clearly Now 21

14 It can be shaped by moulding and, equally important, bacteria find it hard to colonise. An American, Newton Wesley, set out to make contact lenses from PMMA in 1944, and these were for his own use. He suffered badly from a swelling of the eye, but he was in the right location to do something about it because he was a faculty member of the Monroe College of Optometry at Chicago, Illinois. There he teamed up with a bright student George Jessen, and together they worked in the basement of the boarding house where Wesley lived, using a sewing machine as a lathe to shape pieces of Lucite. His PPMA contact lenses were made to cover the whole eye and they were a success. In 1949, he and Jessen began to teach other lens technicians how to make them, and optometrists how to fit and adjust them. By 1955 their company, Wesley- Jessen, was a success and they were spending $500,000 a year on advertising. They also engaged in long-term research, regularly checking 350 of their customers who wore their lens. Meanwhile a Kevin Tuohy was working on an even simpler idea: that the contact lens need only cover the cornea of the eye and he patented such a one in June His lenses were a better fit, were more comfortable to wear and, what was most unexpected, they stayed in place and did not move around the eye ball as one might have expected. Contact lenses made from PPMA are now history. The reason is that they deprive the cornea of oxygen, which it must get directly from the air because the cornea has no blood vessels, and the lack of oxygen can eventually cause damage. What replaced PPMA was another transparent plastic that was gas permeable and which had been discovered in Prague, Czechoslovakia, in the early 1950s. Polymer chemists Otto Wichterle and Drahoslav Lim had modified PPMA by attaching water-attracting groups to the polymer chain. The new material was called HEMA (short for hydroxyethyl methyl methacrylate) and they had originally intended using the polymer to make artificial blood vessels, but when Wichterle dislodged some which had congealed at the bottom of a test-tube he noticed how like a contact lens it was. He had inadvertently made the first soft lens. HEMA is known as a hydrogel, which means that it is a substance that attracts water and holds it in a framework of polymer molecules. Although its softness was a real benefit, HEMA still did not allow significantly more oxygen to penetrate through to the cornea. Nevertheless the lenses, marketed by Bausch and Lomb under the brand 22 Better Looking (I): Hair, Eyes, Teeth, Nails

15 name Soflens, were put on the market in 1971 and were an instant hit. The drawback was that they could harbour germs and so they needed to be cleaned every evening, ideally with hydrogen peroxide, and treated once a week with an enzyme solution of either papain (extracted from pineapple) or pancreatin (from pork) to remove the fat and protein residues which collect from the tears that lubricate and protect the eyes. These residues deposit on the surface of a lens thereby allowing microbes to grow. Polymer chemists also reformulated HEMA by adding measured amounts of other polymer precursors and then polymerising the mixture to form what is known as a copolymer. Varying ratios of copolymers were tried until a hydrogel was obtained which had all the right features, and in particular a negatively charged surface, so that the contact lens would cling to the film of tears on the surface of the eye. Contact lens wearers now have a choice of improved hydrogel types, and while these are better than the older forms they still rely on water to transport oxygen to the eye. Some have as much as 75% water content and this needs to be high if the lenses are to be worn for extended periods. The problem of making soft lenses breathable was eventually solved by attaching silicone groups to PPMA polymer. Silicones dissolve oxygen very easily, but add too many silicones and the polymer becomes water-repellent, something we might expect because silicones are often used to make water-proofing materials. These new lenses were patented in 1974 and marketed in They were referred to as rigid, gas-permeable lenses. The softness and comfort of the older HEMA lenses had been sacrificed in order to prevent longterm damage to the eyes and they had to be custom made for each individual if they were not to be uncomfortable to wear. Softer hydrogel contact lenses, which also incorporated silicone, became available in 1998 and were immediately popular with sales exceeding $150 million within five years. The trouble was that they sometimes glued themselves to the eyeball because they tended to suck out lipid molecules from the cornea and these acted as an adhesive. How did the chemists of companies like Johnson & Johnson and Novartis achieve the seemingly impossible task of combining polymers that appear to be irreconcilable? HEMA attracts water but does not take up oxygen very well while silicones repel water but absorb any amount of oxygen gas. At first the combination of silicone and hydro- I Can See Clearly Now 23

16 gel gave only an opaque material although that was solved by incorporating nanosized components that are smaller than the wavelengths of light so that they appeared transparent. Today there are various silicone-hydrogel materials on the market with water contents ranging from 25 45% and all having excellent oxygen absorption and transmission. 8) Some contact lenses incorporate a fluoroether, another chemical which is particularly good at absorbing oxygen. Silicone-hydrogel contact lenses can even be worn when asleep, but there are some drawbacks to them, the main one being that they are stiffer, although one type, Acuvue Advance, is only marginally stiffer and stiffness need not necessarily be a problem because increased rigidity makes handling the lenses easier. Another manufacturer, Johnson & Johnson, has minimised stiffness by reducing the amount of silicone and putting a layer of PVP, short for poly(vinyl pyrrolidone), as a wetting agent on to the surface. This PVP layer has been added to overcome one of the major drawbacks of soft lenses which is that they can dry up the eye, as many as half their users reporting this discomfort, which is sufficiently irritating to cause many of them to discontinue wearing them. Another way to counteract dryness is to expose the lenses to a gas plasma which creates a permanent ultrathin layer of silicate on their surface, this being formed from the silicone. The resulting silicate does not attract lipids and has increased wettability. Acuvue Advance also blocks out ultraviolet rays (UV), filtering out more than 90% of UVA, and 99% of the UVB rays that are more dangerous to the eye. (These lenses are no substitute for protective goggles which some workers wear to screen their eyes from UV light.) Some disposable contact lenses, such as Acuvue-1-day, are meant to be changed every day, while some, such as Focus1 2 week, produced by Ciba Vision, last longer. The daily ritual of cleaning contact lenses puts many off from wearing them but there are some that can safely be left in the eye for a week, and there are some experimental ones that have been left as long as three months. Ted Reid of Texas Tech University Health Science Centre in Lubbock,Texas, has found that this becomes possible if the lenses are coated with a selenium compound, and the coating need only be one molecule thick. The coating binds itself 8) Nathan Ravi of Washington School of Medicine in St Louis, Missouri, has developed a hydrogel that can be injected into the eye, there to form a new lens to replace a diseased or ageing one. The research is as yet only in its early stages. 24 Better Looking (I): Hair, Eyes, Teeth, Nails

17 chemically to the lens and tests have shown that it can remain in place for as long as two years. These lenses have yet to be approved by the FDA for sale to the public. A Gleaming Smile You may be looking good, thanks to your hair, and seeing better, thanks to contact lenses, but when you smile at the boy or girl of your dreams, are you spoiling your chances by having discoloured teeth? If you suspect that this may be so, then chemistry can help. Unsightly teeth or not, you should think yourself lucky that you are part of this generation. Much earlier generations had a hard time with their teeth as we can see from their remains. A few people in antiquity had the benefit of dental care because we know from mummies that there were dentists in ancient Egypt 4000 years ago. Although they did little more than pull rotten teeth, they sometimes plugged the hole left behind with gold to which they attached a false tooth made of ivory. Their skills were passed on to later civilizations such as the Etruscans and Romans, who developed more sophisticated techniques. Etruscan dentists of the sixth century BC were the first to construct gold bridgework to which they attached artificial teeth made of bone or ivory to fill the gaps left by extracted teeth. Not only did these look good but they clearly were strong enough to eat with. Dentistry in the West declined in the Dark Ages ( AD) and did not really emerge again until tooth decay and toothache became a major problem from the 1600s onwards, due mainly to cheap sugar imported from the plantations of the New World. Sugar can be converted to acid by bacteria that breed in plaque, the film of protein that collects on our teeth, and the acid corrodes the tooth enamel forming cavities in which yet more bacteria can thrive. Dentists did little more than pull out rotten and painful teeth, of which there were many, but they eventually started to make false ones to fill the gaps. Some even used human teeth for this purpose and in 1781 a practitioner of Gerard Street, London, was offering to buy real teeth for 2 each, equivalent to something like 400 (approximately b600 or $700) in today s money, provided they were in good condition. (Such teeth were extracted from newly buried corpses by resurrectionsts who dug up bodies to sell to surgeons for their anatomy lec- A Gleaming Smile 25

18 tures.) Other dentists fitted imitation teeth made of porcelain but these, first produced in 1774, were brittle and made an irritating squeaking noise when chewing. Across the Atlantic, George Washington had a set of dentures consisting of hippopotamus ivory into which were mounted teeth made from those of horses and donkeys. The biggest supply of human teeth came as a result of scavengers plundering the bodies of the dead after major battles. The Battle of Waterloo, fought on 18 June 1815, was a particularly fertile hunting ground with around 50,000 casualties to pick from, and dead young men were more likely to have teeth in good condition. Thousands of teeth were extracted and used by dentists in the subsequent years. The dentures made from them were known as Waterloo teeth, and people were proud to be seen wearing them; some were even exported to the US. Later supplies came from the battlefields of the Crimean War of the 1850s, and the American Civil War of the 1860s, although by then it was more common to have dentures made of a stronger type of porcelain which had been invented in London in Throughout history, people have tried to preserve their teeth by cleaning them. Back in the 4 th century BC, Hippocrates suggested doing this with powdered marble, which is calcium carbonate, and indeed this chemical (as chalk) is still used as a mild abrasive in toothpaste. Toothbrushes were invented in China in 1498 and were known in Europe by the 1600s when they were on sale in Paris, as we learn from a letter sent to Sir Ralph Verney in 1649 asking him to buy one while he was visiting that city. They were used in conjunction with tooth powders. More convenient were the early toothpastes, which consisted of powdered chalk, soap, and sugar syrup. Toothpaste was first sold in ceramic pots and then it began to be sold in collapsible tubes that an American artist, John Rand, had invented in 1841 as a way of packaging oil paints. Modern toothpastes have several components: the scouring agent is likely to be powdered calcium phosphate or silica if the paste is a transparent gel and the foaming agent will be sodium lauryl sulfate. 9) This mild surfactant is added to help disperse the toothpaste in the mouth during the brushing action, thereby solubilising the plaque, and preventing any dislodged debris from re-depositing on the teeth. Toothpaste can have a curious side effect in some people, in that it 9) More about this in Chapter Better Looking (I): Hair, Eyes, Teeth, Nails

19 stimulates the bitter taste receptors on the tongue so that drinks like orange juice become very bitter when drunk immediately after cleaning your teeth. Another major ingredient is the humectant which keeps the toothpaste moist by retaining water and this accounts for about a third of the contents. The ones most commonly used for this purpose are glycerol or PEG (short for polyethylene glycol). The minor ingredients in a typical toothpaste are: an artificial sweetener such as saccharin, or the natural sweetener sorbitol; a thickening agent such as carboxymethyl cellulose, or sodium alginate, which is a carbohydrate extracted from seaweed; sodium benzoate, which prevents bacteria from breeding; fluoride, which strengthens the teeth against decay; flavouring, such as peppermint, or oil of wintergreen. The aim of regular brushing is to keep teeth germ-free and looking good. Discolouration, however, comes slowly and cannot be removed by brushing alone. Teeth have a transparent outer layer of enamel which is about 2 mm thick, and an inner layer of white dentine which surrounds the innermost pulp cavity where the nerves are located. Both the enamel and the dentine are calcium phosphate, a mineral that can exist in various forms, that of the enamel layer being hydroxyapatite, which is one of the hardest naturally occurring minerals. When this is exposed to fluoride it forms an even harder mineral: fluoroapatite. Unfortunately both this and hydroxyapatite are slightly porous and this is why teeth become stained by chemicals such as polyphenols and other dark coloured substances that are present in coffee, tea, red wine, bilberries, blueberries, and cigarette smoke. (Staining can also be caused by tetracycline antibiotics, especially when taken by children whose teeth are developing. This type of discoloration is permanent, which is why such antibiotics are now only prescribed for adults.) The answer to discolouration is to bleach the stains using tooth whiteners. An earlier method of doing this was to use nitric acid which is an oxidising agent and capable of removing stains, but it also removed a layer of the enamel as well. Tooth whiteners now rely on hydrogen peroxide as the bleaching agent and sales are in excess of $1.5 billion a year in the US alone, and the rest of world is catching up on A Gleaming Smile 27

20 the fashion for sparkling white teeth, as popularised by young television and movie stars. A dentist can bleach teeth very quickly by using a paste containing 35% hydrogen peroxide, sometimes in combination with a laser beam supposedly to speed up the process, although the need for this is questionable and stains will be gone within the hour. The paste is applied and rinsed off several times during the treatment, and it has to be carried out by a dentist because hydrogen peroxide of this strength can damage the lining of the mouth if not carefully applied. Dentists can also provide a treatment to be used at home. They make a mould of the teeth into which a strip of peroxide gel can be inserted and then pressed against the teeth. This nightguard can even been worn while sleeping, thereby speeding up the whitening process. For those who prefer a less expensive way of bleaching their teeth, there are products which contain a chemical that reacts with water to release hydrogen peroxide. This chemical is carbamide peroxide, also known as urea peroxide, 10) and this is the ingredient in several overthe-counter whitening agents. Carbamide peroxide is made from urea and hydrogen peroxide. The former chemical is perfectly safe because it is a normal end-product of our body s metabolism and is one of the ways we dispose of unwanted nitrogenous material via our urine. In earlier times it was even prescribed by doctors because of its diuretic action, in other words it encouraged the body to remove excess water by stimulating the kidneys. When carbamide peroxide is in contact with water it releases its hydrogen peroxide which then gets to work, although a lot of this is lost to enzyme breakdown before it can do its job. This is why over-the-counter tooth whitening products need to be applied many times to achieve maximum effect. The most convenient way of whitening teeth is to stick a polyethylene strip bearing a peroxide gel to the teeth and leave it there for 30 minutes. If this procedure is repeated every day then after a couple of weeks the teeth will be noticeably whiter. Those who engage in tooth whitening should be aware that it has a weakening effect on the enamel. This was reported at a meeting of the US Materials Research Society in Boston in November 2005 by Michelle Dickinson who works for Hysitron, an instrument maker based in Minneapolis. This company has developed a piece of equipment capable of measuring the hardness profile of teeth across the enamel and dentine 10) It also has trade names such as Exterol, Hyperol, Perhydrit, etc. See also urea in Glossary. 28 Better Looking (I): Hair, Eyes, Teeth, Nails

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